The present application relates to a transmission cable for use in radio frequency (RF) electrical and/or magnetic fields. It finds particular application in conjunction with magnetic resonance imaging (MRI) system and will be described with particular reference to galvanic isolation when guided through radio frequency (RF) electrical and/or magnetic fields of an MR imaging system.
A MR imaging system is often used for the examination and treatment of patients. By such a system, the nuclear spins of the body tissue to be examined are aligned by a static main magnetic field B0 and are excited by transverse magnetic fields B1 oscillating in the radiofrequency band. The resulting relaxation signals are exposed to gradient magnetic fields to localize the resultant resonance. The relaxation signals are received in order to form in a known manner a single or multiple dimension image.
Use is made of active interventional devices which are introduced into the patient, for example, it is highly desired to perform interventional procedures under MRI guidance in order to improve therapy outcome and to reduce radiation exposure. Transmission lines or paths are provided for connecting the distal tip and/or other components of the interventional device, such as catheters, needles, stents, imaging coils, guidewires, and the like, with an active unit, notably a power supply, a receiving/transmission device, a control unit, or the like. The active interventional devices usually have to be guided through MR fields which in the case of an MR system includes the B1 field, generated in the form of RF pulses which are transmitted by the RF coil system. Such RF fields may induce common mode signals (currents) in the transmission line and in the surrounding body tissue. Such common mode signal can cause large electric fields. These currents create not only the risk of disturbances or destruction of the accessory device and/or the active unit, but notably they can give rise to substantial heating of the adjacent tissue resulting in potentially severe burns of inner organs or blood/tissue coagulation for the patient.
For example, it is highly desired to perform electrophysiology (EP) interventions under MRI guidance in order to improve therapy outcome and to reduce X-ray exposure. One method to realize RF safe active interventional devices is to segment the transmission line into short, non-resonant segments, which are mechanically connected during the intervention or mechanically disconnected during imaging. However, there is no mean to verify that the line segments are decoupled from one another to ensure safety from RF induced common mode currents, short circuits, or the like.
The present application provides a new and improved system and method which overcomes the above-referenced problems and others.
In accordance with one aspect, a transmission line for use in a radio-frequency and/or magnetic field is presented. The transmission line includes at least two electrically conductive transmission line segments separated by a non-conductive gap. The gap is bridged by an electrically conductive bridge which has two states: a closed state which electrically connects two of the transmission line segments across the non-conductive gap and a open state which electrically disconnects the at least two transmission line segments across the non-conductive gap. An impedance bridge is connected electrically in parallel to the electrically conductive bridge to bridge the non-conductive gaps, each impedance bridge has an impedance which is chosen to suppress radiofrequency (RF) induced current between the line segments. A bridge controller is operatively connected to the conductive bridge to control its one of two states. A measurement unit measures the impedance across the line segments and the impedance bridge while the conductive bridge controlled to be in the open state.
In accordance with another aspect, a method of using a transmission line is presented. The transmission line includes at least a pair of transmission line segments separated by a non-conductive gap. The non-conductive gap is bridged by a conductive bridge which is parallel to an impedance bridge. The method comprises of installing the transmission line in an interventional instrument, such as a catheter. The conductive bridge is controlled to an open state such that the line segments are electrically decoupled. An impedance of the impedance bridge is measured.
One advantage resides in that safety for a patient and equipment is improved.
Still further advantages of the present invention will be appreciated to those of ordinary skill in the art upon reading and understand the following detailed description.